You have to hand it to Harmonix, when it comes to rhythm games, they always seem to be on top of things. While they had success with previous titles, they really changed the industry with Guitar Hero, and kept the momentum going with Guitar Hero 2. When they parted ways with Red Octane they decided it was time to start another revolution with Rock Band, which just landed them a huge $209 million bonus from Viacom.
The payout comes because of a clause that was in the acquisition of the company by Viacom. It stated "to the extent financial results exceed specific contractual targets against a defined gross profit metric through 2008 former Harmonix shareholders will be eligible for incremental earn-out payments with respect to the years ended December 31, 2007 and December 31, 2008."
When you disect all of the lawyer speak, it means that in the event that Harmonix does better than expected, they'll get a big fat check. Which is exactly what they did. With all of the great DLC they have been releasing, I don't think the Rock Band money-machine is going to be slowing down any time soon.